Allow setting metadata atomically on initial upload

[broccolihighkicks]

The "create and then update" workflow does not work well in some cases.

E.g. I am setting obj.cache_control = Some("no-store".to_string()); obj.update().await to prevent GCS's default forced cache of one hour (which cannot be circumvented from the browser).

Two issues:

• 1. Sometimes that update request succeeds but the metadata of the object is not updated for some reason (I think this may be an error Google's end when writing the same object many times).
• 2. If I am creating/updating the object, it may have been replaced by the time the update runs.

Is it possible to add metadata to Object::create so that this happens in one single request instead of two?

This would solve the two issues above by making object-creation-with-metadata a single atomic step.

[ThouCheese]

Hi @broccolihighkicks, sorry for the late response. This is something that can definitely be implemented. Currently, cloud_storage uses the 'Single request' upload scheme. This would require us the switch to multipart form uploads (described just below). Since reqwest supports multipart form requests out of the box, an implementation of this should be straightforward. Would you like to contribute on this?